2540 SOLIDS*
2540 A. Introduction
Solids refer to matter suspended or dissolved in water or
wastewater. Solids may affect water or effluent quality adversely
in a number of ways. Waters with high dissolved solids generally
are of inferior palatability and may induce an unfavorable phys-
iological reaction in the transient consumer. For these reasons, a
limit of 500 mg dissolved solids/L is desirable for drinking
waters. Highly mineralized waters also are unsuitable for many
industrial applications. Waters high in suspended solids may be
esthetically unsatisfactory for such purposes as bathing. Solids
analyses are important in the control of biological and physical
wastewater treatment processes and for assessing compliance
with regulatory agency wastewater effluent limitations.
1.
Definitions
“Total solids” is the term applied to the material residue left in
the vessel after evaporation of a sample and its subsequent
drying in an oven at a defined temperature. Total solids includes
“total suspended solids,” the portion of total solids retained by a
filter, and “total dissolved solids,” the portion that passes through
the filter.
The type of filter holder, the pore size, porosity, area, and thick-
ness of the filter and the physical nature, particle size, and amount
of material deposited on the filter are the principal factors affecting
separation of suspended from dissolved solids. “Dissolved solids” is
the portion of solids that passes through a filter of 2.0
m (or
smaller) nominal pore size under specified conditions. “Suspended
solids” is the portion retained on the filter.
“Fixed solids” is the term applied to the residue of total,
suspended, or dissolved solids after heating to dryness for a
specified time at a specified temperature. The weight loss on
ignition is called “volatile solids.” Determinations of fixed and
volatile solids do not distinguish precisely between inorganic
and organic matter because the loss on ignition is not confined to
organic matter. It includes losses due to decomposition or vol-
atilization of some mineral salts. Better characterization of or-
ganic matter can be made by such tests as total organic carbon
(Section 5310), BOD (Section 5210), and COD (Section 5220).
“Settleable solids” is the term applied to the material settling
out of suspension within a defined period. It may include floating
material, depending on the technique (2540F.3b).
2.
Sources of Error and Variability
Sampling, subsampling, and pipeting two-phase or three-phase
samples may introduce serious errors. Make and keep such samples
homogeneous during transfer. Use special handling to insure sample
integrity when subsampling. Mix small samples with a magnetic
stirrer. If suspended solids are present, pipet with wide-bore pipets.
If part of a sample adheres to the sample container, consider this in
evaluating and reporting results. Some samples dry with the forma-
tion of a crust that prevents water evaporation; special handling is
required to deal with this. Avoid using a magnetic stirrer with
samples containing magnetic particles.
The temperature at which the residue is dried has an important
bearing on results, because weight losses due to volatilization of
organic matter, mechanically occluded water, water of crystalli-
zation, and gases from heat-induced chemical decomposition, as
well as weight gains due to oxidation, depend on temperature
and time of heating. Each sample requires close attention to
desiccation after drying. Minimize opening desiccator because
moist air enters. Some samples may be stronger desiccants than
those used in the desiccator and may take on water.
Residues dried at 103 to 105°C may retain not only water of
crystallization but also some mechanically occluded water. Loss
of CO
2
will result in conversion of bicarbonate to carbonate.
Loss of organic matter by volatilization usually will be very
slight. Because removal of occluded water is marginal at this
temperature, attainment of constant weight may be very slow.
Residues dried at 180 ⫾2°C will lose almost all mechanically
occluded water. Some water of crystallization may remain, es-
pecially if sulfates are present. Organic matter may be lost by
volatilization, but not completely destroyed. Loss of CO
2
results
from conversion of bicarbonates to carbonates and carbonates
may be decomposed partially to oxides or basic salts. Some
chloride and nitrate salts may be lost. In general, evaporating and
drying water samples at 180°C yields values for dissolved solids
closer to those obtained through summation of individually
determined mineral species than the dissolved solids values
secured through drying at the lower temperature.
To rinse filters and filtered solids and to clean labware use
Type III water. Special samples may require a higher quality
water; see Section 1080.
Results for residues high in oil or grease may be questionable
because of the difficulty of drying to constant weight in a
reasonable time.
To aid in quality assurance, analyze samples in duplicate. Dry
samples to constant weight if possible. This entails multiple
drying-cooling-weighing cycles for each determination.
Analyses performed for some special purposes may demand
deviation from the stated procedures to include an unusual constit-
uent with the measured solids. Whenever such variations of tech-
nique are introduced, record and present them with the results.
3.
Sample Handling and Preservation
Use resistant-glass or plastic bottles, provided that the material
in suspension does not adhere to container walls. Begin analysis
as soon as possible because of the impracticality of preserving
the sample. Refrigerate sample at 4°C up to the time of analysis
to minimize microbiological decomposition of solids. Preferably
do not hold samples more than 24 h. In no case hold sample more
than 7 d. Bring samples to room temperature before analysis.
* Approved by Standard Methods Committee, 1997. Editorial revisions, 2011.
Joint Task Group: 20th Edition—Brannon H. Wilder (chair), Harold S. Costa,
Christine M. Kosmowski, William E. Purcell.
1
4.
Selection of Method
Methods B through F are suitable for the determination of
solids in potable, surface, and saline waters, as well as domestic
and industrial wastewaters in the range up to 20 000 mg/L.
Method G is suitable for the determination of solids in sedi-
ments, as well as solid and semisolid materials produced during
water and wastewater treatment.
5. Bibliography
THERIAULT, E.J. & H.H. WAGENHALS. 1923. Studies of representative
sewage plants. Pub. Health Bull. No. 132.
U.S. ENVIRONMENTAL PROTECTION AGENCY. 1979. Methods for Chemical
Analysis of Water and Wastes. Publ. 600/4-79-020, rev. Mar. 1983.
Environmental Monitoring and Support Lab., U.S. Environmental
Protection Agency, Cincinnati, Ohio.
2540 B. Total Solids Dried at 103–105°C
1.
General Discussion
a. Principle: A well-mixed sample is evaporated in a weighed dish
and dried to constant weight in an oven at 103 to 105°C. The increase
in weight over that of the empty dish represents the total solids. The
results may not represent the weight of actual dissolved and suspended
solids in wastewater samples (see above).
b. Interferences: Highly mineralized water with a significant con-
centration of calcium, magnesium, chloride, and/or sulfate may be
hygroscopic and require prolonged drying, proper desiccation, and
rapid weighing. Exclude large, floating particles or submerged agglom-
erates of nonhomogeneous materials from the sample if it is determined
that their inclusion is not desired in the final result. Disperse visible
floating oil and grease with a blender before withdrawing a sample
portion for analysis. Because excessive residue in the dish may form a
water-trapping crust, limit sample to no more than 200 mg residue (see
2540A.2).
c. Quality control (QC): The QC practices considered to be an
integral part of each method are summarized in Tables 2020:I
and II.
2.
Apparatus
a. Evaporating dishes: Dishes of 100-mL capacity made of
one of the following materials:
1) Porcelain, 90-mm diam.
2) Platinum—Generally satisfactory for all purposes.
3) High-silica glass.*
b. Muffle furnace for operation at 550°C.
c. Steam bath.
d. Desiccator, provided with a desiccant containing a color
indicator of moisture concentration or an instrumental indicator.
e. Drying oven, for operation at 103 to 105°C.
f. Analytical balance, capable of weighing to 0.1 mg.
g. Magnetic stirrer with TFE stirring bar.
h. Wide-bore pipets.†
i. Graduated cylinder.
j. Low-form beaker.‡
3.
Procedure
a. Preparation of evaporating dish: If volatile solids are to be
measured ignite clean evaporating dish at 550°C for1hina
muffle furnace. If only total solids are to be measured, heat clean
dish to 103 to 105°C for 1 h. Store and cool dish in desiccator
until needed. Weigh immediately before use.
b. Sample analysis: Choose a sample volume that will yield a
residue between 2.5 and 200 mg. Pipet a measured volume of well-
mixed sample, during mixing, to a preweighed dish. For homogeneous
samples, pipet from the approximate midpoint of the container but not
in the vortex. Choose a point both middepth and midway between wall
and vortex. Evaporate to dryness on a steam bath or in a drying oven.
Stir sample with a magnetic stirrer during transfer. If necessary, add
successive sample portions to the same dish after evaporation. When
evaporating in a drying oven, lower temperature to approximately 2°C
below boiling to prevent splattering. Dry evaporated sample for at least
1 h in an oven at 103 to 105°C, cool dish in desiccator to balance
temperature, and weigh. Repeat cycle of drying, cooling, desiccating,
and weighing until a constant weight is obtained, or until weight change
is less than 4% of previous weight or 0.5 mg, whichever is less. When
weighing dried sample, be alert to change in weight due to air exposure
and/or sample degradation. Analyze at least 10% of all samples in
duplicate. Duplicate determinations should agree within 5% of their
average weight.
4.
Calculation
mg total solids/L ⫽(A⫺B)⫻1000
sample volume, mL
where:
A⫽weight of dried residue ⫹dish, mg, and
B⫽weight of dish, mg.
5.
Precision
Single-laboratory duplicate analyses of 41 samples of water
and wastewater were made with a standard deviation of differ-
ences of 6.0 mg/L.
6. Bibliography
SYMONS,G.E.&B.MOREY. 1941. The effect of drying time on the
determination of solids in sewage and sewage sludges. Sewage
Works J. 13:936.
* Vycor, product of Corning Glass Works, Corning, NY, or equivalent.
† Kimble Nos. 37005 or 37034B, or equivalent.
‡ Class B or better.
SOLIDS (2540)/Total Solids Dried at 103–105°C
2
SOLIDS (2540)/Total Solids Dried at 103–105°C
2540 C. Total Dissolved Solids Dried at 180°C
1.
General Discussion
a. Principle: A well-mixed sample is filtered through a stan-
dard glass fiber filter, and the filtrate is evaporated to dryness in
a weighed dish and dried to constant weight at 180°C. The
increase in dish weight represents the total dissolved solids. This
procedure may be used for drying at other temperatures.
The results may not agree with the theoretical value for solids
calculated from chemical analysis of sample (see above). Ap-
proximate methods for correlating chemical analysis with dis-
solved solids are available.
1
The filtrate from the total suspended
solids determination (2540D) may be used for determination of
total dissolved solids.
b. Interferences: See 2540A.2 and 2540B.1b. Highly mineralized
waters with a considerable calcium, magnesium, chloride, and/or sul-
fate content may be hygroscopic and require prolonged drying, proper
desiccation, and rapid weighing. Samples high in bicarbonate require
careful and possibly prolonged drying at 180°C to insure complete
conversion of bicarbonate to carbonate. Because excessive residue in
the dish may form a water-trapping crust, limit sample to no more than
200 mg residue.
c. Quality control (QC): The QC practices considered to be an
integral part of each method are summarized in Tables 2020:I
and II.
2.
Apparatus
Apparatus listed in 2540B.2a– h is required, and in addition:
a. Glass-fiber filter disks* without organic binder.
b. Filtration apparatus: One of the following, suitable for the
filter disk selected:
1) Membrane filter funnel.
2) Gooch crucible, 25-mL to 40-mL capacity, with Gooch
crucible adapter.
3) Filtration apparatus with reservoir and coarse (40- to
60-
m) fritted disk as filter support.†
c. Suction flask, of sufficient capacity for sample size selected.
d. Drying oven, for operation at 180 ⫾2°C.
3.
Procedure
a. Preparation of glass-fiber filter disk: If pre-prepared glass
fiber filter disks are used, eliminate this step. Insert disk with
wrinkled side up into filtration apparatus. Apply vacuum and
wash disk with three successive 20-mL volumes of reagent-
grade water. Continue suction to remove all traces of water.
Discard washings.
b. Preparation of evaporating dish: If volatile solids are to be
measured, ignite cleaned evaporating dish at 550°C for1hina
muffle furnace. If only total dissolved solids are to be measured,
heat clean dish to 180 ⫾2°Cfor1hinanoven. Store in
desiccator until needed. Weigh immediately before use.
c. Selection of filter and sample sizes: Choose sample volume
to yield between 2.5 and 200 mg dried residue. If more than 10
min are required to complete filtration, increase filter size or
decrease sample volume.
d. Sample analysis: Stir sample with a magnetic stirrer and pipet
a measured volume onto a glass-fiber filter with applied vacuum.
Wash with three successive 10-mL volumes of reagent-grade water,
allowing complete drainage between washings, and continue suc-
tion for about 3 min after filtration is complete. Transfer total filtrate
(with washings) to a weighed evaporating dish and evaporate to
dryness on a steam bath or in a drying oven. If necessary, add
successive portions to the same dish after evaporation. Dry evapo-
rated sample for at least1hinanoven at 180 ⫾2°C, cool in a
desiccator to balance temperature, and weigh. Repeat drying cycle
of drying, cooling, desiccating, and weighing until a constant weight
is obtained or until weight change is less than 4% of previous
weight or 0.5 mg, whichever is less. Analyze at least 10% of all
samples in duplicate. Duplicate determinations should agree within
5% of their average weight. If volatile solids are to be determined,
follow procedure in 2540E.
4.
Calculation
mg total dissolved solids/L ⫽(A⫺B)⫻1000
sample volume, mL
where:
A⫽weight of dried residue ⫹dish, mg, and
B⫽weight of dish, mg.
5.
Precision
Single-laboratory analyses of 77 samples of a known of 293
mg/L were made with a standard deviation of differences of
21.20 mg/L.
6. Reference
1. SOKOLOFF, V.P. 1933. Water of crystallization in total solids of water
analysis. Ind. Eng. Chem., Anal. Ed. 5:336.
7. Bibliography
HOWARD, C.S. 1933. Determination of total dissolved solids in water
analysis. Ind. Eng. Chem., Anal. Ed. 5:4.
U.S. GEOLOGICAL SURVEY. 1974. Methods for Collection and Analysis of
Water Samples for Dissolved Minerals and Gases. Techniques of
Water-Resources Investigations, Book 5, Chap. A1. U.S. Geologi-
cal Surv., Washington, D.C.
* Whatman grade 934AH; Gelman type A/E; Millipore type AP40; E-D Scientific
Specialties grade 161; Environmental Express Pro Weigh; or other products that
give demonstrably equivalent results. Practical filter diameters are 2.2 to 12.5 cm.
† Gelman No. 4201 or equivalent.
SOLIDS (2540)/Total Dissolved Solids Dried at 180°C
3
SOLIDS (2540)/Total Dissolved Solids Dried at 180°C
2540 D. Total Suspended Solids Dried at 103–105°C
1.
General Discussion
a. Principle: A well-mixed sample is filtered through a
weighed standard glass-fiber filter and the residue retained on the
filter is dried to a constant weight at 103 to 105°C. The increase
in weight of the filter represents the total suspended solids. If the
suspended material clogs the filter and prolongs filtration, it may
be necessary to increase the diameter of the filter or decrease the
sample volume. To obtain an estimate of total suspended solids,
calculate the difference between total dissolved solids and total
solids.
b. Interferences: See 2540A.2 and 2540B.1b. Exclude
large floating particles or submerged agglomerates of nonho-
mogeneous materials from the sample if it is determined that
their inclusion is not representative. Because excessive resi-
due on the filter may form a water-entrapping crust, limit the
sample size to that yielding no more than 200 mg residue. For
samples high in dissolved solids thoroughly wash the filter to
ensure removal of dissolved material. Prolonged filtration
times resulting from filter clogging may produce high results
owing to increased colloidal materials captured on the
clogged filter.
c. Quality control (QC): The QC practices considered to be an
integral part of each method are summarized in Tables 2020:I
and II.
2.
Apparatus
Apparatus listed in 2540B.2 and C.2 is required, except for
evaporating dishes, steam bath, and 180°C drying oven. In
addition:
Aluminum weighing dishes.
3.
Procedure
a. Preparation of glass-fiber filter disk: If pre-prepared glass
fiber filter disks are used, eliminate this step. Insert disk with
wrinkled side up in filtration apparatus. Apply vacuum and wash
disk with three successive 20-mL portions of reagent-grade
water. Continue suction to remove all traces of water, turn
vacuum off, and discard washings. Remove filter from filtration
apparatus and transfer to an inert aluminum weighing dish. If a
Gooch crucible is used, remove crucible and filter combination.
Dry in an oven at 103 to 105°C for 1 h. If volatile solids are to
be measured, ignite at 550°C for 15 min in a muffle furnace.
Cool in desiccator to balance temperature and weigh. Repeat
cycle of drying or igniting, cooling, desiccating, and weighing
until a constant weight is obtained or until weight change is less
than 4% of the previous weighing or 0.5 mg, whichever is less.
Store in desiccator until needed.
b. Selection of filter and sample sizes: Choose sample volume
to yield between 2.5 and 200 mg dried residue. If volume filtered
fails to meet minimum yield, increase sample volume up to 1 L.
If complete filtration takes more than 10 min, increase filter
diameter or decrease sample volume.
c. Sample analysis: Assemble filtering apparatus and filter and
begin suction. Wet filter with a small volume of reagent-grade water
to seat it. Stir sample with a magnetic stirrer at a speed to shear
larger particles, if practical, to obtain a more uniform (preferably
homogeneous) particle size. Centrifugal force may separate parti-
cles by size and density, resulting in poor precision when point of
sample withdrawal is varied. While stirring, pipet a measured vol-
ume onto the seated glass-fiber filter. For homogeneous samples,
pipet from the approximate midpoint of container but not in vortex.
Choose a point both middepth and midway between wall and
vortex. Wash filter with three successive 10-mL volumes of re-
agent-grade water, allowing complete drainage between washings,
and continue suction for about 3 min after filtration is complete.
Samples with high dissolved solids may require additional wash-
ings. Carefully remove filter from filtration apparatus and transfer to
an aluminum weighing dish as a support. Alternatively, remove the
crucible and filter combination from the crucible adapter if a Gooch
crucible is used. Dry for at least1hat103to105°C in an oven, cool
in a desiccator to balance temperature, and weigh. Repeat the cycle
of drying, cooling, desiccating, and weighing until a constant weight
is obtained or until the weight change is less than 4% of the previous
weight or 0.5 mg, whichever is less. Analyze at least 10% of all
samples in duplicate. Duplicate determinations should agree within
5% of their average weight. If volatile solids are to be determined,
treat the residue according to 2540E.
4.
Calculation
mg total suspended solids/L ⫽(A⫺B)⫻1000
sample volume, mL
where:
A⫽weight of filter ⫹dried residue, mg, and
B⫽weight of filter, mg.
5.
Precision
The standard deviation was 5.2 mg/L (coefficient of variation
33%) at 15 mg/L, 24 mg/L (10%) at 242 mg/L, and 13 mg/L
(0.76%) at 1707 mg/L in studies by two analysts of four sets of
10 determinations each.
Single-laboratory duplicate analyses of 50 samples of water
and wastewater were made with a standard deviation of differ-
ences of 2.8 mg/L.
6. Bibliography
DEGEN, J. & F.E. NUSSBERGER. 1956. Notes on the determination of
suspended solids. Sewage Ind. Wastes 28:237.
CHANIN, G., E.H. CHOW, R.B. ALEXANDER &J.POWERS. 1958. Use of
glass fiber filter medium in the suspended solids determination.
Sewage Ind. Wastes 30:1062.
NUSBAUM, I. 1958. New method for determination of suspended solids.
Sewage Ind. Wastes 30:1066.
SMITH, A.L. & A.E. GREENBERG. 1963. Evaluation of methods for deter-
mining suspended solids in wastewater. J. Water Pollut. Control
Fed. 35:940.
SOLIDS (2540)/Total Suspended Solids Dried at 103–105°C
4
SOLIDS (2540)/Total Suspended Solids Dried at 103–105°C
WYCKOFF, B.M. 1964. Rapid solids determination using glass fiber
filters. Water Sewage Works 111:277.
NATIONAL COUNCIL OF THE PAPER INDUSTRY FOR AIR AND STREAM IMPROVE-
MENT. 1975. A Preliminary Review of Analytical Methods for the
Determination of Suspended Solids in Paper Industry Effluents for
Compliance with EPA-NPDES Permit Terms. Spec. Rep. No. 75-
01. National Council of the Paper Industry for Air & Stream
Improvement, New York, N.Y.
NATIONAL COUNCIL OF THE PAPER INDUSTRY FOR AIR AND STREAM IMPROVE
MENT. 1977. A Study of the Effect of Alternate Procedures on
Effluent Suspended Solids Measurement. Stream Improvement
Tech. Bull. No. 291, National Council of the Paper Industry for Air
& Stream Improvement, New York, N.Y.
TREES, C.C. 1978. Analytical analysis of the effect of dissolved solids on
suspended solids determination. J. Water Pollut. Control Fed. 50:
2370.
2540 E. Fixed and Volatile Solids Ignited at 550°C
1.
General Discussion
a. Principle: The residue from Method B, C, or D is ignited to
constant weight at 550°C. The remaining solids represent the fixed
total, dissolved, or suspended solids while the weight lost on ignition is
the volatile solids. The determination is useful in control of wastewater
treatment plant operation because it offers a rough approximation of the
amount of organic matter present in the solid fraction of wastewater,
activated sludge, and industrial wastes.
b. Interferences: Negative errors in the volatile solids may
be produced by loss of volatile matter during drying. Deter-
mination of low concentrations of volatile solids in the pres-
ence of high fixed solids concentrations may be subject to
considerable error. In such cases, measure for suspect volatile
components by another test, for example, total organic carbon
(Section 5310). Highly alkaline residues may react with silica
in sample or silica-containing crucibles.
c. Quality control (QC): The QC practices considered to be an
integral part of each method are summarized in Tables 2020:I
and II.
2.
Apparatus
See Sections 2540B.2, C.2, and D.2.
3.
Procedure
Ignite residue produced by Method 2540B, C, or D to constant
weight in a muffle furnace at a temperature of 550°C. Ignite a
blank glass fiber filter along with samples. Have furnace up to
temperature before inserting sample. Usually, 15 to 20 min
ignition are required for 200 mg residue. However, more than
one sample and/or heavier residues may overtax the furnace and
necessitate longer ignition times. Let dish or filter disk cool
partially in air until most of the heat has been dissipated. Trans-
fer to a desiccator for final cooling in a dry atmosphere. Do not
overload desiccator. Weigh dish or disk as soon as it has cooled
to balance temperature. Repeat cycle of igniting, cooling, desic-
cating, and weighing until a constant weight is obtained or until
weight change is less than 4% or 0.5 mg, whichever is less.
Analyze at least 10% of all samples in duplicate. Duplicate
determinations should agree within 5% of their average weight.
Weight loss of the blank filter is an indication of unsuitability of
a particular brand or type of filter for this analysis.
4.
Calculation
mg volatile solids/L ⫽(A⫺B)⫻1000
sample volume, mL
mg fixed solids/L ⫽(B⫺C)⫻1000
sample volume, mL
where:
A⫽weight of residue ⫹dish before ignition, mg,
B⫽weight of residue ⫹dish or filter after ignition, mg, and
C⫽weight of dish or filter, mg.
5.
Precision
The standard deviation was 11 mg/L at 170 mg/L volatile total
solids in studies by three laboratories on four samples and 10
replicates. Bias data on actual samples cannot be obtained.
2540 F. Settleable Solids
1.
General Discussion
Settleable solids in surface and saline waters as well as domestic and
industrial wastes may be determined and reported on either a volume
(mL/L) or a weight (mg/L) basis.
The QC practices considered to be an integral part of each method
are summarized in Table 2020:II.
2.
Apparatus
The volumetric test requires only an Imhoff cone. The
gravimetric test requires all the apparatus listed in 2540D.2
and a glass vessel with a minimum diameter of 9 cm.
SOLIDS (2540)/Settleable Solids
5
SOLIDS (2540)/Settleable Solids
6
7
1
/
7
100%